Stable and complete overcoming of MDR1/P-glycoprotein-mediated multidrug resistance in human gastric carcinoma cells by RNA interference

Strategies to enhance the response of liver cancer to pharmacological treatments

In contrast to other types of cancers, there is no available efficient pharmacological treatment to improve the outcomes of patients suffering from major primary liver cancers, i.e., hepatocellular carcinoma and cholangiocarcinoma. This dismal situation is partly due to the existence in these tumors of many different and synergistic mechanisms of resistance, accounting for the lack of response of these patients, not only to classical chemotherapy but also to more modern pharmacological agents based on the inhibition of tyrosine kinase receptors (TKIs) and the stimulation of the immune response against the tumor using immune checkpoint inhibitors (ICIs). This review summarizes the efforts to develop strategies to overcome this severe limitation, including searching for novel drugs derived from synthetic, semisynthetic, or natural products with vectorial properties against therapeutic targets to increase drug uptake or reduce drug export from cancer cells. Besides, immunotherapy is a promising line of research that is already starting to be implemented in clinical practice. Although less successful than in other cancers, the foreseen future for this strategy in treating liver cancers is considerable. Similarly, the pharmacological inhibition of epigenetic targets is highly promising. Many novel "epidrugs," able to act on "writer," "reader," and "eraser" epigenetic players, are currently being evaluated in preclinical and clinical studies. Finally, gene therapy is a broad field of research in the fight against liver cancer chemoresistance, based on the impressive advances recently achieved in gene manipulation. In sum, although the present is still dismal, there is reason for hope in the non-too-distant future.

Thermodynamic and cellular studies of doxorubicin/daunorubicin loaded by a DNA tetrahedron for diagnostic imaging, chemotherapy, and gene therapy

The combined diagnostic imaging, chemotherapy, and gene therapy based on DNA nanocarriers can reduce the toxic side effects and overcome multidrug resistance (MDR). In this study, we designed an antisense oligonucleotides (ASOs)-linked DNA tetrahedron (ASOs-TD). The detection limit of ASOs-TD for MDR1 mRNA was 0.05 μM. By using fluorescence spectroscopy and isothermal titration calorimetry (ITC), the interactions between doxorubicin (DOX) /daunorubicin (DAU) and ASOs-TD were investigated. The number of binding sites (n), binding constant (Ka), entropy change (ΔSo), enthalpy change (ΔHo) and Gibbs free energy change (ΔGo) were obtained. The intercalation of DOX/DAU with ASOs-TD was demonstrated by differential scanning calorimetry (DSC) and quenching researches of potassium ferricyanide K4[Fe(CN)6]. The in vitro release rate of DOX/DAU loaded in ASOs-TD was accelerated by deoxyribonuclease I (DNase I). In vitro cytotoxicity proved the good gene therapy effect of ASOs-TD and the increased cytotoxicity of DOX/DAU to MCF-7/ADR cells. The results of confocal laser scanning microscope (CLSM) suggested that ASOs-TD could effectively identify drug-resistant cells due to its good imaging ability for MDR1 mRNA. This work offers theoretical significance for overcoming MDR using DNA nanostructures which combine diagnostic imaging, chemotherapy, and gene therapy.

Expression of GnT-III decreases chemoresistance via negatively regulating P-glycoprotein expression: Involvement of the TNFR2-NF-κB signaling pathway

The phenomenon of multidrug resistance (MDR) is called chemoresistance with respect to the treatment of cancer, and it continues to be a major challenge. The role of N-glycosylation in chemoresistance, however, remains poorly understood. Here, we established a traditional model for adriamycin resistance in K562 cells, which are also known as K562/adriamycin-resistant (ADR) cells. Lectin blot, mass spectrometry, and RT-PCR analysis showed that the expression levels of N-acetylglucosaminyltransferase III (GnT-III) mRNA and its products, bisected N-glycans, are significantly decreased in K562/ADR cells, compared with the levels in parent K562 cells. By contrast, the expression levels of both P-glycoprotein (P-gp) and its intracellular key regulator, NF-κB signaling, are significantly increased in K562/ADR cells. These upregulations were sufficiently suppressed by the overexpression of GnT-III in K562/ADR cells. We found that the expression of GnT-III consistently decreased chemoresistance for doxorubicin and dasatinib, as well as activation of the NF-κB pathway by tumor necrosis factor (TNF) α, which binds to two structurally distinct glycoproteins, TNF receptor 1 (TNFR1) and TNF receptor 2 (TNFR2), on the cell surface. Interestingly, our immunoprecipitation analysis revealed that only TNFR2, but not TNFR1, contains bisected N-glycans. The lack of GnT-III strongly induced TNFR2's autotrimerization without ligand stimulation, which was rescued by the overexpression of GnT-III in K562/ADR cells. Furthermore, the deficiency of TNFR2 suppressed P-gp expression while it increased GnT-III expression. Taken together, these results clearly show that GnT-III negatively regulates chemoresistance via the suppression of P-gp expression, which is regulated by the TNFR2-NF/κB signaling pathway.

Aptamer-functionalized Hybrid Nanoparticles to Enhance the Delivery of Doxorubicin into Breast Cancer Cells by Silencing P-glycoprotein

OBJECTIVE

The MDR of metastatic breast cancer cells is accompanied by the overexpression of P-gp transporter. This study has been focused to determine whether silencing the expression of P-gp by aptamer-labeled siRNA nanoparticles could enhance the delivery of doxorubicin into breast cancer cells in culture.

METHODOLOGY

The nanoparticle F-31 was prepared using DOTAP, cholesterol, and PLGA, and then incorporating Mal-PEG to facilitate aptamer-binding. The nanoparticles were surface-functionalized with aptamer A6, which targets Her-2 receptors overexpressed on the surface of breast cancer cells.

RESULTS

This study has shown that the uptake of Dox by Dox-resistant 4T1-R is significantly less than Dox-sensitive 4T1-S which is partly attributed to the higher expression of drug-efflux pump P-gp on the surface of the resistant cells. The targeted knockdown of P-gp has been enhanced when the particles carrying P-gp siRNA was labeled with aptamer. Concurrently, the uptake of Dox into the Dox-resistant 4T1-R breast cancer cells has increased significantly when the P-gp was silenced by P-gp siRNA-encapsulated aptamer-labeled nanoparticles.

CONCLUSIONS

This preliminary study concludes that downregulating P-gp expression by targeted delivery of P-gp siRNA using aptamer-labeled lipid-based hybrid nanoparticles could effectively increase the intracellular trafficking of doxorubicin in Dox-resistant mouse breast cancer cells.

Probing cholesterol binding and translocation in P-glycoprotein

P-glycoprotein (Pgp) is a biomedically important member of the ABC transporter superfamily that mediates multidrug resistance in various cancer types. Substrate binding and transport in Pgp are modulated by the presence of cholesterol in the membrane. Structural information on cholesterol binding sites and mechanistic details of its redistribution are, however, largely unknown. In this study, a set of 40 independent molecular dynamics (MD) simulations of Pgp embedded in cholesterol-rich lipid bilayers are reported, totaling 8 μs, enabling extensive sampling of cholesterol-protein interactions in Pgp. Clustering analyses of the ensemble of cholesterol molecules (∼5740) sampled around Pgp in these simulations reveal specific and asymmetric cholesterol-binding regions formed by the transmembrane (TM) helices TM1-6 and TM8. Notably, not all the putative cholesterol binding sites identified by MD can be predicted by the primary sequence based cholesterol-recognition amino acid consensus (CRAC) or inverted CRAC (CARC) motifs, an observation that we attribute to inadequacy of these motifs to account for binding sites formed by remote amino acids in the sequence that can still be spatially adjacent to each other. Binding of cholesterol to Pgp occurs more frequently through its rough β-face formed by the two protruding methyl groups, whereas the opposite smooth α-face prefers packing alongside the membrane lipids. One full and two partial cholesterol flipping events between the two leaflets of the bilayer mediated by the surface of Pgp are also captured in these simulations. All flipping events are observed in a region formed by helices TM1, TM2, and TM11, featuring two full and two partial CRAC/CARC motifs, with Tyr49 and Tyr126 identified as key residues interacting with cholesterol during this event. Our study is the first to report direct observation of unconventional cholesterol translocation on the surface of Pgp, providing a secondary transport model for the known flippase activity of ABC exporters of cholesterol. This article is part of a Special Issue entitled: Molecular biophysics of membranes and membrane proteins.

Combined effects of octreotide and cisplatin on the proliferation of side population cells from anaplastic thyroid cancer cell lines

Anaplastic thyroid cancer (ATC) represents the most aggressive subtype of thyroid cancer and has a poor prognosis. In addition to surgery, chemotherapy is an important treatment for ATC; however, the therapeutic effects of current chemotherapies for ATC are not particularly promising. There is a high proportion of side population (SP) cells in ATC, which may be a reason for its drug resistance. In the present study, the antitumor activities of combined octreotide (OCT) and cisplatin (DDP) on the proliferation and apoptosis of ATC SP cells were evaluated. First, SP cells from 8305C and BHT101 cell lines were detected and sorted. Following in vitro culture for 1 week, cluster of differentiation (CD)44, CD133, ATP-binding cassette (ABC) subfamily B member 1 (ABCB1), ABC subfamily G member 2 (ABCG2) and somatostatin receptor expression was detected to characterize the SP cells. An MTT assay was performed to investigate the combined effects on 8305C-SP cell proliferation in vitro, and a mouse model was used to investigate the combined effects on 8305C-SP cell proliferation in vivo. Annexin V/propidium iodide staining was used to investigate the combined effects on 8305C-SP cell apoptosis. Chemotherapeutic drug resistance-associated protein expression and apoptosis-associated protein expression were also detected following combined treatment. As a result, SP cells were identified in 8305C and BHT101 cells, and the proportion of 8305C-SP cells was increased compared with that of BTH101-SP cells. SP cells have enhanced proliferation, tumorigenicity and drug resistance compared with main population cells. The combined treatment of OCT with DDP suppressed the proliferation of 8305C-SP cells in vitro and in vivo, and induced 8305C-SP cell apoptosis. Combined treatment decreased the ABCB1 and ABCG2 expression by SP cells and activated mitochondrial apoptotic signaling, resulting in cell apoptosis. In conclusion, these data support the hypothesis that combined treatment with OCT and DDP induces ATC cell apoptosis and suppresses cell proliferation. These data provide a theoretical basis for further combined chemotherapy clinical applications.

Lidocaine Induces Apoptosis and Suppresses Tumor Growth in Human Hepatocellular Carcinoma Cells In Vitro and in a Xenograft Model In Vivo

Background

Recent epidemiologic studies have focused on the potential beneficial effects of regional anesthetics, and the differences in cancer prognosis may be the result of anesthetics on cancer biologic behavior. However, the function and underlying mechanisms of lidocaine in hepatocellular carcinoma both in vitro and in vivo have been poorly studied.

Methods

Human HepG2 cells were treated with lidocaine. Cell viability, colony formation, cell cycle, and apoptosis were assessed. The effects of lidocaine on apoptosis-related and mitogen-activated protein kinase protein expression were evaluated by Western blot analysis. The antitumor activity of lidocaine in hepatocellular carcinoma with or without cisplatin was investigated with in vitro experiments and also with animal experiments.

Results

Lidocaine inhibited the growth of HepG2 cells in a dose- and time-dependent manner. The authors also found that lidocaine arrested cells in the G0/G1 phase of the cell cycle (63.7 ± 1.7% vs. 72.4 ± 3.2%; P = 0.0143) and induced apoptosis (1.7 ± 0.3% vs. 5.0 ± 0.7%; P = 0.0009). Lidocaine may exert these functions by causing an increase in Bax protein and activated caspase-3 and a corresponding decrease in Bcl-2 protein through the extracellular signal-regulated kinase 1/2 and p38 pathways. More importantly, for the first time, xenograft experiments (n = 8 per group) indicated that lidocaine suppressed tumor development (P < 0.0001; lidocaine vs. control) and enhanced the sensitivity of cisplatin (P = 0.0008; lidocaine plus cisplatin vs. cisplatin).

Conclusions

The authors’ findings suggest that lidocaine may exert potent antitumor activity in hepatocellular carcinoma. Furthermore, combining lidocaine with cisplatin may be a novel treatment option for hepatocellular carcinoma.

Molecular mechanisms of chemoresistance in gastric cancer

Gastric cancer is the fourth most common cancer and the second leading cause of cancer deaths worldwide. Chemotherapy is one of the major treatments for gastric cancer, but drug resistance limits the effectiveness of chemotherapy, which results in treatment failure. Resistance to chemotherapy can be present intrinsically before the administration of chemotherapy or it can develop during chemotherapy. The mechanisms of chemotherapy resistance in gastric cancer are complex and multifactorial. A variety of factors have been demonstrated to be involved in chemoresistance, including the reduced intracellular concentrations of drugs, alterations in drug targets, the dysregulation of cell survival and death signaling pathways, and interactions between cancer cells and the tumor microenvironment. This review focuses on the molecular mechanisms of chemoresistance in gastric cancer and on recent studies that have sought to overcome the underlying mechanisms of chemoresistance.

Transporter effects on cell permeability in drug delivery

INTRODUCTION

The role of drug transporters as one of the determinants of cellular drug permeability has become increasingly evident. Despite the lipophilicity of a drug molecule as rate-limiting factor for passive diffusion across biological membranes, carrier-mediated and active transport have gained attention over the years. A better understanding of the effects and roles of these influx transporters towards transmembrane permeability of a drug molecule need to be delineated for drug development and delivery. Areas covered: This review focuses on findings relative to role of transporters in drug absorption and bioavailability. Particularly the areas demanding further research have been emphasized. This review will also highlight various transporters expressed on vital organs and their effects on drug pharmacokinetics. Expert opinion: Significant efforts have been devoted to understand the role of transporters, their iterative interplay with metabolizing enzymes through molecular enzymology, binding and structure-activity relationship studies. A few assays such as parallel artificial membrane permeation assay (PAMPA) have been developed to analyze drug transport across phospholipid membranes. Although large web-accessible databases on tissue selective expression profiles at transcriptomic as well as proteomic are available, there is a need to collocate the scattered literature on the role of transporters in drug development and delivery.

Co-delivery of doxorubicin and arsenite with reduction and pH dual-sensitive vesicle for synergistic cancer therapy

Drug resistance is the underlying cause for therapeutic failure in clinical cancer chemotherapy. A prodrug copolymer mPEG-PAsp(DIP-co-BZA-co-DOX) (PDBD) was synthesized and assembled into a nanoscale vesicle comprising a PEG corona, a reduction and pH dual-sensitive hydrophobic membrane and an aqueous lumen encapsulating doxorubicin hydrochloride (DOX·HCl) and arsenite (As). The dual stimulation-sensitive design of the vesicle gave rise to rapid release of the physically entrapped DOX·HCl and arsenite inside acidic lysosomes, and chemically conjugated DOX inside the cytosol with high glutathione (GSH) concentration. In the optimized concentration range, arsenite previously recognized as a promising anticancer agent from traditional Chinese medicine can down-regulate the expressions of anti-apoptotic and multidrug resistance proteins to sensitize cancer cells to chemotherapy. Consequently, the DOX-As-co-loaded vesicle demonstrated potent anticancer activity. Compared to the only DOX-loaded vesicle, the DOX-As-co-loaded one induced more than twice the apoptotic ratio of MCF-7/ADR breast cancer cells at a low As concentration (0.5 μM), due to the synergistic effects of DOX and As. The drug loading strategy integrating chemical conjugation and physical encapsulation in stimulation-sensitive carriers enabled efficient drug loading in the formulation.

Effective co-delivery of doxorubicin and curcumin using a glycyrrhetinic acid-modified chitosan-cystamine-poly(ε-caprolactone) copolymer micelle for combination cancer chemotherapy

A glycyrrhetinic acid-modified chitosan-cystamine-poly(ε-caprolactone) copolymer (PCL-SS-CTS-GA) micelle was developed for the co-delivery of doxorubicin (DOX) and curcumin (CCM) to hepatoma cells. Glycyrrhetinic acid (GA) was used as a targeting unit to ensure specific delivery. Co-encapsulation of DOX and CCM was facilitated by the incorporation of poly(ε-caprolactone) (PCL) groups. The highest drug loading content was 19.8% and 8.9% (w/w) for DOX and CCM, respectively. The PCL-SS-CTS-GA micelle presented a spherical or ellipsoidal geometry with a mean diameter of approximately 110nm. The surface charge of the micelle changed from negative to positive, when the pH value of the solution decreased from 7.4 to 6.8. Meanwhile, it also exhibited a character of redox-responsive drug release and GA/pH-mediated endocytosis in vitro. In simulated body fluid with 10mM glutathione, the release rate in 12h was 80.6% and 67.2% for DOX and CCM, respectively. The cell uptake of micelles was significantly higher at pH 6.8 than pH 7.4. The combined administration of DOX and CCM was facilitated by PCL-SS-CTS-GA micelle. Results showed that there was strong synergic effect between the two drugs. The PCL-SS-CTS-GA micelle might turn into a promising and effective carrier for improved combination chemotherapy.

Gene Therapeutic Approaches to Overcome ABCB1-Mediated Drug Resistance

Multidrug resistance (MDR) to pharmaceutical active agents is a common clinical problem in patients suffering from cancer. MDR is often mediated by over expression of trans-membrane xenobiotic transport molecules belonging to the superfamily of ATP-binding cassette (ABC)-transporters. This protein family includes the classical MDR-associated transporter ABCB1 (MDR1/P-gp). Inhibition of ABC-transporters by low molecular weight compounds in cancer patients has been extensively investigated in clinical trials, but the results have been disappointing. Thus, in the last decades alternative experimental therapeutic strategies for overcoming MDR were under extensive investigation. These include gene therapeutic approaches applying antisense-, ribozyme-, RNA interference-, and CRISPR/Cas9-based techniques. Various delivery strategies were used to reverse MDR in different tumor models in vitro and in vivo. Results and conclusions of these gene therapeutic studies will be discussed.

ZHX2 enhances the cytotoxicity of chemotherapeutic drugs in liver tumor cells by repressing MDR1 via interfering with NF-YA

We previously reported the tumor suppressor function of Zinc-fingers and homeoboxes 2 (ZHX2) in hepatocellular carcinoma (HCC). Other studies indicate the association of increased ZHX2 expression with improved response to high dose chemotherapy in multiple myeloma. Here, we aim to test whether increased ZHX2 levels in HCC cells repress multidrug resistance 1(MDR1) expression resulting in increased sensitivity to chemotherapeutic drugs. We showed evidence that increased ZHX2 levels correlated with reduced MDR1 expression and enhanced the cytotoxicity of CDDP and ADM in different HCC cell lines. Consistently, elevated ZHX2 significantly reduced ADM efflux in HepG2 cells and greatly increased the CDDP-mediated suppression of liver tumor growth in vivo. Furthermore, immunohistochemical staining demonstrated the inverse correlation of ZHX2 and MDR1 expression in HCC tissues. Luciferase report assay showed that ZHX2 repressed the MDR1 promoter activity, while knockdown of NF-YA or mutating the NF-Y binding site eliminated this ZHX2-mediated repression of MDR1 transcription. Co-IP and ChIP assay further suggested that ZHX2 interacted with NF-YA and reduced NF-Y binding to the MDR1 promoter. Taken together, we clarify that ZHX2 represses NF-Y-mediated activation of MDR1 transcription and, in doing so, enhances the effects of chemotherapeutics in HCC cells both in vitro and in vivo.

Reversal of multidrug resistance by co-delivery of paclitaxel and lonidamine using a TPGS and hyaluronic acid dual-functionalized liposome for cancer treatment

Multidrug resistance (MDR) remains the primary issue in cancer therapy, which is characterized by the overexpressed P-glycoprotein (P-gp)-included efflux pump or the upregulated anti-apoptotic proteins. In this study, a D-alpha-tocopheryl poly (ethylene glycol 1000) succinate (TPGS) and hyaluronic acid (HA) dual-functionalized cationic liposome containing a synthetic cationic lipid, 1,5-dioctadecyl-N-histidyl-L-glutamate (HG2C18) was developed for co-delivery of a small-molecule chemotherapeutic drug, paclitaxel (PTX) with a chemosensitizing agent, lonidamine (LND) to treat the MDR cancer. It was demonstrated that the HG2C18 lipid contributes to the endo-lysosomal escape of the liposome following internalization for efficient intracellular delivery. The TPGS component was confirmed able to elevate the intracellular accumulation of PTX by inhibiting the P-gp efflux, and to facilitate the mitochondrial-targeting of the liposome. The intracellularly released LND suppressed the intracellular ATP production by interfering with the mitochondrial function for enhanced P-gp inhibition, and additionally, sensitized the MDR breast cancer (MCF-7/MDR) cells to PTX for promoted induction of apoptosis through a synergistic effect. Functionalized with the outer HA shell, the liposome preferentially accumulated at the tumor site and showed a superior antitumor efficacy in the xenograft MCF-7/MDR tumor mice models. These findings suggest that this dual-functional liposome for co-delivery of a cytotoxic drug and an MDR modulator provides a promising strategy for reversal of MDR in cancer treatment.

Co-delivery of Sildenafil (Viagra(®)) and Crizotinib for synergistic and improved anti-tumoral therapy

PURPOSE

Cancer multi-drug resistance is a major issue associated with current anti-tumoral therapeutics. In this work, Crizotinib an anti-tumoral drug approved for the treatment of non-small lung cancer in humans, and Sildenafil (Viagra(®)), were loaded into micellar carriers to evaluate the establishment of a possible synergistic anti-tumoral effect in breast cancer cells.

METHODS

Micellar carriers comprised by PEG-PLA block co-polymers were formulated by the solvent displacement method in which the simultaneous encapsulation of Crizotinib and Sildenafil was promoted. Encapsulation efficiency was analyzed by a new UPLC method validated for this combination of compounds. Micelle physicochemical characterization and cellular uptake were characterized by light scattering and confocal microscopy. The bio- and hemocompatibility of the carriers was also evaluated. MCF-7 breast cancer cells were used to investigate the synergistic anti-tumoral effect.

RESULTS

Our results demonstrate that this particular combination induces massive apoptosis of breast cancer cells. The co-delivery of Crizotinib and Sildenafil was only possible due to the high encapsulation efficiency of the micellar systems (>70%). The micelles with size ranging between 93 and 127 nm were internalized by breast cancer cells and subsequently released their payload in the intracellular compartment. The results obtained demonstrated that the delivery of both drugs by micellar carriers led to a 2.7 fold increase in the anti-tumoral effect, when using only half of the concentration that is required when free drugs are administered.

CONCLUSIONS

Altogether, co-delivery promoted a synergistic effect and demonstrated for the first time the potential of PEG-PLA-Crizotinib-Sildenafil combination for application in cancer therapy.

Reversal of ATP-binding cassette drug transporter activity to modulate chemoresistance: why has it failed to provide clinical benefit?

Enhanced drug extrusion from cells due to the overexpression of the ATP-binding cassette (ABC) drug transporters inhibits the cytotoxic effects of structurally diverse and mechanistically unrelated anticancer agents and is a major cause of multidrug resistance (MDR) of human malignancies. Multiple compounds can suppress the activity of these efflux transporters and sensitize resistant tumor cells, but despite promising preclinical and early clinical data, they have yet to find a role in oncologic practice. Based on the knowledge of the structure, function, and distribution of MDR-related ABC transporters and the results of their preclinical and clinical evaluation, we discuss probable reasons why these inhibitors have not improved the outcome of therapy for cancer patients. We also outline new MDR-reversing strategies that directly target ABC transporters or circumvent relevant signaling pathways.

Molecular cloning and characterization of a P-glycoprotein from the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Macrocyclic lactones such as abamectin and ivermectin constitute an important class of broad-spectrum insecticides. Widespread resistance to synthetic insecticides, including abamectin and ivermectin, poses a serious threat to the management of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), a major pest of cruciferous plants worldwide. P-glycoprotein (Pgp), a member of the ABC transporter superfamily, plays a crucial role in the removal of amphiphilic xenobiotics, suggesting a mechanism for drug resistance in target organisms. In this study, PxPgp1, a putative Pgp gene from P. xylostella, was cloned and characterized. The open reading frame (ORF) of PxPgp1 consists of 3774 nucleotides, which encodes a 1257-amino acid peptide. The deduced PxPgp1 protein possesses structural characteristics of a typical Pgp, and clusters within the insect ABCB1. PxPgp1 was expressed throughout all developmental stages, and showed the highest expression level in adult males. PxPgp1 was highly expressed in midgut, malpighian tubules and testes. Elevated expression of PxPgp1 was observed in P. xylostella strains after they were exposed to the abamectin treatment. In addition, the constitutive expressions of PxPgp1 were significantly higher in laboratory-selected and field-collected resistant strains in comparison to their susceptible counterpart.

Induction of the ABC-Transporters Mdr1/P-gp (Abcb1), Mrp1 (Abcc1), and Bcrp (Abcg2) during Establishment of Multidrug Resistance Following Exposure to Mitoxantrone

Resistance to mitoxantrone is often associated with enhanced drug efflux mediated by members of the superfamily of adenosinetriphosphate-binding cassette (ABC) transporters, i.e. MDR1/P-gp (ABCB1), MRP1 (ABCC1), or BCRP (ABCG2). So far it is unclear whether the same ABC-transporter is always activated from the beginning of mitoxantrone treatment to the end of drug exposure. Here, we demonstrate that the expression of all three extrusion pumps is induced by increasing levels of mitoxantrone resistance, but in the end, merely the overexpression of a dominant single drug transporter, i.e. Mdr1/P-gp, is realized. This upregulation of Mdr1/P-gp was reflected by amplification of the Mdr1/P-gp encoding gene. Short mitoxantrone exposure demonstrated that upregulation of two different transporters, Mdr1/P-gp and Bcrp, was induced. The data indicate that mitoxantrone treatment influences the expression of several ABC-transporters, but in the end, merely a single extrusion pump will be dominant.

Effect of shRNA-mediated inhibition of Nanog gene expression on the behavior of human gastric cancer cells

The aim of the present study was to employ RNA interference (RNAi) technology to construct and select shRNA-Nanog recombinant plasmids for the inhibition of Nanog gene expression and transfer these plasmids into the human gastric cancer cell line, SGC-7901, as well as to detect the expression of Nanog and the effects on the proliferation, migration, invasion, cell cycle and apoptosis of SGC-7901 cells. The pshRNA-Nanog interference plasmids were constructed and used to transfect SGC-7901 cells using lipofectamine. The expression of the Nanog gene was detected by fluorescence microscopy, RT-PCR and western blotting, and the most markedly inhibited group was identified. The SGC-7901 cells were transfected with recombinant shRNA-Nanog plasmids from the most markedly inhibited group using lipofectamine and the effect on proliferation was determined by CCK-8 assay. The migration and invasion of the SGC-7901 cells was determined by Transwell assays, while the cell cycle and apoptosis were analyzed by flow cytometry. The group with the highest inhibition rate was successfully constructed and identified. It was observed that the proliferation, invasion and migration capacity of the cells was reduced, that the cell cycle was arrested at the S phase and that apoptosis was significantly increased. The Nanog gene in gastric cancer cells is closely associated with cell proliferation, the cell cycle, apoptosis and migration and invasion abilities. The present study establishes the foundations for a novel approach for the genetic treatment of gastric cancer.

Role of RNA interference in research of multidrug resistance in gastric cancer

Gastric cancer is one of the most common malignant tumors in the world. Chemotherapy is the main treatment for gastric cancer after operation. However, multidrug resistance of tumor cells always reduces its effectiveness and influences the prognosis of patients directly. For this reason, more and more scientific researchers have been dedicated to the in-depth study of multidrug resistance in gastric cancer. RNA interference allows specific and effective inhibition of the expression of target genes and has been gradually applied to gene treatment for multidrug resistance in gastric cancer. The widespread use of RNA interference in recent years has led to many achievements. This article aims to review the role of RNA interference in research of multidrug resistance in gastric cancer.

Activated ERM protein plays a critical role in drug resistance of MOLT4 cells induced by CCL25

We have previously demonstrated that the CCR9/CCL25 signaling pathway plays an important role in drug resistance in human acute T-lymphocytic leukemia (T-ALL) by inducing activation of ERM protein with polarized distribution in T-ALL cell line MOLT4. However, the mechanism of action of the activated ERM protein in the drug resistance of MOLT4 cells induced by CCL25 remains uncharacterized. Here we investigated the mechanism of CCR9/CCL25-initiated drug resistance in CCR9-high-expressing T-ALL cells. Our results showed that 1) the function of P-gp was increased after treatment with CCL25; 2) P-gp colocalized and co-immunoprecipitated with p-ERM and F-actin in CCL25 treated cells; and 3) ERM-shRNA conferred drug sensitivity coincident with release of ERM interactions with P-gp and F-actin after treatment with CCL25. These data suggest it is pivotal that P-gp associate with the F-actin cytoskeleton through p-ERM in CCR9/CCL25 induced multidrug resistance of T-ALL cells. Strategies aimed at inhibiting P-gp-F-actin cytoskeleton association may be helpful in increasing the efficiency of therapies in T-ALL.

Thymosin beta 15A (TMSB15A) is a predictor of chemotherapy response in triple-negative breast cancer

Background:

Biomarkers predictive of pathological complete response (pCR) to neoadjuvant chemotherapy (NACT) of breast cancer are urgently needed.

Methods:

Using a training/validation approach for detection of predictive biomarkers in HER2-negative breast cancer, pre-therapeutic core biopsies from four independent cohorts were investigated: Gene array data were analysed in fresh frozen samples of two cohorts (n=86 and n=55). Quantitative reverse transcription polymerase chain reaction (qRT–PCR) was performed in formalin-fixed, paraffin-embedded (FFPE) samples from two neoadjuvant phase III trials (GeparTrio, n=212, and GeparQuattro, n=383).

Results:

A strong predictive capacity of thymosin beta 15 (TMSB15A) gene expression was evident in both fresh frozen cohorts (P<0.0001; P<0.0042). In the GeparTrio FFPE training cohort, a significant linear correlation between TMSB15A expression and pCR was apparent in triple-negative breast cancer (TNBC) (n=61, P=0.040). A cutoff point was then defined that divided TNBC into a low and a high expression group (pCR rate 16.0% vs 47.2%). Both linear correlation of TMSB15A mRNA levels (P=0.017) and the pre-defined cutoff point were validated in 134 TNBC from GeparQuattro (pCR rate 36.8% vs 17.0%, P=0.020). No significant predictive capacity was observed in luminal carcinomas from GeparTrio and GeparQuattro.

Conclusion:

In TNBC, TMSB15A gene expression analysis might help to select patients with a high chance for pCR after NACT.

Research Spotlight: Delivery of therapeutic RNA molecules to cancer cells by bacteria

Delivery of RNA-based therapeutics, for example RNA interference (RNAi) effectors, to target cells is one of the major obstacles for the development of RNA-based therapies. Since it has been known for a long time that bacteria can mediate tumor shrinkage, it was obvious to use nonpathogenic bacteria to produce and deliver therapeutic RNA molecules into target cells to induce RNAi. During the last years, two bacteria-based concepts were developed for this strategy, transkingdom RNAi (tkRNAi) and bacteria-mediated RNAi (bmRNAi). The first concept, tkRNAi, delivers RNAi effectors into target cells by invasive bacteria, which themselves produce therapeutic shRNAs. The bmRNAi technology utilizes invasive bacteria conveying RNAi effector-encoding DNA constructs that will act as a matrix for transcription of these sequences in the target cell by the host cell’s transcription machinery.

Bacterial delivery of RNAi effectors: transkingdom RNAi

RNA interference (RNAi) represents a high effective mechanism for specific inhibition of mRNA expression. Besides its potential as a powerful laboratory tool, the RNAi pathway appears to be promising for therapeutic utilization. For development of RNA interference (RNAi)-based therapies, delivery of RNAi-mediating agents to target cells is one of the major obstacles. A novel strategy to overcome this hurdle is transkingdom RNAi (tkRNAi). This technology uses non-pathogenic bacteria, e.g. Escherichia coli, to produce and deliver therapeutic short hairpin RNA (shRNA) into target cells to induce RNAi. A first-generation tkRNAi-mediating vector, TRIP, contains the bacteriophage T7 promoter for expression regulation of a therapeutic shRNA of interest. Furthermore, TRIP has the Inv locus from Yersinia pseudotuberculosis that encodes invasin, which permits natural noninvasive bacteria to enter β1-integrin-positive mammalian cells and the HlyA gene from Listeria monocytogenes, which produces listeriolysin O. This enzyme allows the therapeutic shRNA to escape from entry vesicles within the cytoplasm of the target cell. TRIP constructs are introduced into a competent non-pathogenic Escherichia coli strain, which encodes T7 RNA polymerase necessary for the T7 promoter-driven synthesis of shRNAs. A well-characterized cancer-associated target molecule for different RNAi strategies is ABCB1 (MDR1/P-glycoprotein, MDR1/P-gp). This ABC-transporter acts as a drug extrusion pump and mediates the "classical" ABCB1-mediated multidrug resistance (MDR) phenotype of human cancer cells which is characterized by a specific cross resistance pattern. Different ABCB1-expressing MDR cancer cells were treated with anti-ABCB1 shRNA expression vector bearing E. coli. This procedure resulted in activation of the RNAi pathways within the cancer cells and a considerable down regulation of the ABCB1 encoding mRNA as well as the corresponding drug extrusion pump. Accordingly, drug accumulation was enhanced in the pristine drug-resistant cancer cells and the MDR phenotype was reversed. By means of this model the data provide the proof-of-concept that tkRNAi is suitable for modulation of cancer-associated factors, e.g. ABCB1, in human cancer cells.

Jet-injection of short hairpin RNA-encoding vectors into tumor cells

The use of the RNA interference (RNAi) through the expression of small hairpin RNA (shRNA) is a promising approach for efficient gene silencing for therapeutic applications. In this chapter, we describe the in vivo reversal of the classical MDR1/P-glycoprotein (MDR1/P-gp)-mediated multidrug resistance (MDR) phenotype by shRNA. For local intratumoral delivery of naked shRNA-encoding vector constructs, the nonviral jet-injection was used. This jet-injector system uses compressed air to inject small volumes (5-10 muL) of naked nucleic acid solutions into tumor tissues. Furthermore, the design of the jet-injector allows multiple injections. Under our experimental design, the delivery of plasmid DNA encoding anti-MDR shRNA by jet-injection into human MDR1/P-gp overexpressing MaTu/ADR breast cancer xenografts resulted in a decrease of MDR1 mRNA expression level to more than 90%. Accordingly, the corresponding MDR1/P-gp protein is no longer detectable in the tumors after anti-MDR1 shRNA vector injection. Furthermore, combination of two intratumoral jet-injections of anti-MDR1 shRNA vectors with two intravenous administrations of doxorubicin is sufficient for a complete reversal of the MDR phenotype in association with tumor growth inhibition.

Overcoming multidrug resistance by RNA interference

The ATP-binding cassette (ABC)-transporter P-glycoprotein (Pgp, also known as ABCB1) is the best characterized factor involved in multidrug resistance (MDR) of cancer cells. Pgp, which is encoded by the MDR1 gene, acts as a membrane-embedded drug extrusion pump for multiple structurally unrelated cytotoxic drugs. Inhibition of the pump activity of Pgp by low-molecular weight pharmacologically active compounds as a method to reverse MDR in cancer patients has been studied extensively, but so far clinical trials have generally been disappointing. Thus, experimental strategies for overcoming MDR are under investigation. These approaches include the application of the RNA interference (RNAi) technology. RNAi is a physiological mechanism triggered by small double-stranded RNA molecules resulting in a sequence-specific gene-silencing. Besides its potential for development of novel therapeutics, RNAi also offers the possibility for specific inhibition of cellular targets in functional investigations. For specific inhibition of Pgp by triggering the RNAi pathway, transient gene-silencing by application of small interfering RNA (siRNA), and stable inhibition by transfection of MDR cancer cells with short hairpin RNA (shRNA) encoding expression cassettes encoded on plasmid DNA are described. Efficacy of RNAi on MDR1 mRNA expression level is determined by quantitative real-time RT-PCR and Northern blot. The consequences of RNAi on protein expression level are measured by Western blot and immunohistochemistry. The effects on the drug extrusion activity are measured by a drug accumulation assay based on flow cytometry, and reversal of the drug-resistant phenotype by assessment of drug-specific IC(50)-values by a cell proliferation assay based on colorimetry.

Suppression of the multidrug transporter P-glycoprotein using RNA interference in cultured rat astrocytes induced by coriaria lactone

The overexpression of the multidrug resistance gene (MDR-1) and its translational product p-glycoprotein (P-gp) may play an important role in pharmacoresistant epilepsy. We established the rat astrocyte model overexpressing P-gp induced by coriaria lactone and successfully nucleofected it with the siRNA-hairpin expression vector pSIREN-shuttle designed to target MDR-1B mRNA. The mRNA expression of MDR-1B gene was mostly knock down by 67.70% (p<0.01). The expression of P-gp in experimental group was significantly lower than that in negative control (p<0.05), and the rhodamine efflux ratio of experimental group (23.08%) was remarkably lower than that of negative control (78.35%, p<0.01). We first employed RNA interfering to the drug resistance reversal of refractory epilepsy and this may provide a new way for refractory epilepsy remedy.

Therapeutic potential of RNA interference in drug-resistant cancers

Resistance including multidrug resistance to chemotherapy is a common clinical problem in patients suffering from cancer. Multidrug resistance is often mediated by overexpression of transmembrane xenobiotic transport molecules belonging to the superfamily of ATP-binding cassette (ABC)-transporters. Inhibition of ABC-transporters by low-molecular weight compounds in cancer patients has been extensively investigated in clinical trials, but the results have been disappointing. Thus, alternative experimental therapeutic strategies for overcoming multidrug resistance are under investigation. These include the application of RNA interference (RNAi) technology. Various RNAi strategies were applied to reverse multidrug resistance in different tumor models in vitro and in vivo. Results and conclusions of these RNAi studies as well as their potential impact for the development of potential RNAi therapeutics will be discussed.

Inhibition of P-glycoprotein over-expression by shRNA-mdr1b in rat astrocytes

The development of multiple drug resistance (MDR) is a significant problem in epilepsy therapy. The primary factor responsible for antiepileptic drug (AEDs) resistance is the over-expression of the MDR gene product, P-glycoprotein (Pgp). To model a therapeutic approach for decreasing drug resistance in patients with intractable epilepsy, we established a model of coriaria lactone (CL) induced Pgp overexpression in rat astrocytes and administered a recombinant adenovirus Ad5-EGFP-shRNA1-U6 to deliver an anti-mdr1b short hairpin RNA (shRNA) for 5 days. We then investigated the gene-silencing effects of shRNA by quantitative real-time RT-PCR, Western-blot, and Rho123 accumulation assay. The results showed that over-expression of mdr1b and Pgp was successfully suppressed, the ability of intracellular Rho123 retention was increased, and drug efflux was decreased in the adenovirus treated astrocytes. In conclusion, MDR was reversed in rat astrocyte model. These findings may be favorable for developing new therapeutic strategies for treating intractable epilepsy.

Silencing the breast cancer resistance protein expression and function in caco-2 cells using lentiviral vector-based short hairpin RNA

A series of stable breast cancer resistance protein (BCRP, ABCG2) knockdown cell lines were produced by transduction of Caco-2 cells with lentiviral vector-based short hairpin RNA (shRNA). Caco-2 cell is a human intestinal-derived cell line widely used to study intestinal drug absorption. Caco-2 expresses three apical drug efflux transporters: BCRP, P-glycoprotein (P-gp; ABCB1), and multidrug resistance protein 2 (MRP2, ABCC2). BCRP and P-gp in particular play a significant role in pharmacokinetics because of their expression at several key interfaces. Overexpression of BCRP in cancer cells may also be a mechanism of tumor resistance to chemotherapeutic drugs. The goal of this study was to engineer and characterize Caco-2 cell clones with stable knockdown of BCRP expression. The shRNA/BCRP lentiviral particles were used to infect a stable clone of Caco-2 cells. Expression of BCRP was monitored using quantitative polymerase chain reaction (qPCR), Western blotting, immunofluorescence microscopy, and bidirectional transport of probe substrates, estrone-3-sulfate (E3S), and pheophorbide A (PhA). Based on qPCR, expression of BCRP mRNA was knocked down in five clones with a maximum of 97% silencing in clone D. Silencing of BCRP gene expression was maintained for at least 25 passages. Expression of BCRP protein was also reduced significantly. Functionally, BCRP knockdown was reflected in significant reduction of the efflux ratio of E3S and PhA. Clone D in particular should be a useful model for identifying and characterizing P-gp substrates and inhibitors without interference from BCRP and/or MRP2. In addition, it can be used in conjunction with wild-type or vector control Caco-2 cells to identify BCRP substrates.

Calcium carbonate nanoparticle delivering vascular endothelial growth factor-C siRNA effectively inhibits lymphangiogenesis and growth of gastric cancer in vivo

A nonviral gene carrier, calcium carbonate (CaCO3) nanoparticle, was evaluated for efficient in vitro and in vivo delivery of small interfering RNA (siRNA) targeting vascular endothelial growth factor-C (VEGF-C). The chemically synthesized CaCO3 nanoparticle has a 58 nm diameter and +28.6 mV positive surface charge. It is capable of forming a CaCO3 nanoparticle-DNA complex and transferring DNA into targeted cells with high transfection efficiency while effectively protecting the encapsulated DNA from degradation. Furthermore, the CaCO3 nanoparticle-DNA complex has no obvious cytotoxicity for SGC-7901 cells, while a liposome-DNA complex exhibited measurable cytotoxicity. SGC-7901 cells transfected with a VEGF-C-targeted siRNA via CaCO3 nanoparticle exhibit significantly reduced VEGF-C expression as measured by real-time PCR and enzyme-linked immunosorbent assay; whereas no decrease in VEGF-C expression is observed in cells treated by control transfection. Transfection of SGC-7901 cells with VEGF-C siRNA via CaCO3 nanoparticle also dramatically suppresses tumor lymphangiogenesis, tumor growth and regional lymph-node metastasis in subcutaneous xenografts. Significant downregulation of VEGF-C messenger RNA expression in a subcutaneous xenograft derived from VEGF-C siRNA-treated SGC-7901 cells was confirmed by real-time PCR as compared to controls. We conclude that CaCO3 nanoparticle is a novel and nonviral system for effective delivery of siRNA for cancer gene therapy.

Complete In Vivo Reversal of the Multidrug Resistance Phenotype by Jet-injection of Anti-MDR1 Short Hairpin RNA-encoding Plasmid DNA

Triggering the RNA interference (RNAi) pathway by inducing the expression of short hairpin RNA (shRNA) molecules has become a promising tool for efficient silencing of a given gene in gene therapy applications. In this study, shRNA encoding DNA was utilized to reverse the classical MDR1/P-glycoprotein (MDR1/P-gp)-mediated multidrug resistance (MDR) phenotype in vivo. For the first time, the nonviral jet-injection technology was applied for delivering naked shRNA-vector constructs for direct intratumoral in vivo transfer. The highly efficient anti-MDR1 shRNA expression vectors were applied twice in the human MDR1/P-gp overexpressing MaTu/ADR cancer xenograft-bearing mice, and twice in the corresponding drug-sensitive parental MaTu tumor xenograft bearing mice as well. Two days after anti-MDR1 shRNA vector injection, the expression level of the MDR1 messenger RNA (mRNA) was decreased by more than 90% and the corresponding MDR1/P-gp protein was no longer detectable in the tumors. Two jet-injections of anti-MDR1 shRNA vectors into the tumors, combined with two intravenous (IV) administrations of doxorubicin, were sufficient to achieve complete reversal of the drug-resistant phenotype. The data show that jet-injection delivery of shRNA-expressing vectors is effective in reversing MDR1/P-gp-mediated MDR in vivo, and is therefore a promising strategy for making tumors with an MDR1/Pgp-dependent MDR phenotype revert to a drug-sensitive state.

FANCD2 depletion sensitizes cancer cells repopulation ability in vitro

Inactivation of Fanconi anemia/BRCA pathway in some cancers causes increased sensitivity to various drugs used for chemo-therapy. Several approaches have been suggested to artificially disrupt this pathway for better treatment. In our study, we have utilized RNA interference technique to knock-down the expression of FANCD2 and sensitize cancer cells undergoing treatment with DNA damaging agents. For this purpose, we transiently depleted FANCD2 by siRNA in a number of breast, bladder, or liver cancer cell lines and screened for mitomycin C or gamma-irradiation sensitivity changes. We could show that knocking-down FANCD2 gene expression increases sensitivity of cancer cells to mitomycin C and to less extent to gamma-rays. Importantly, this effect strongly correlates to repopulation ability of cancer cells and those cell lines with significant FANCD2 depletion revealed decreased recurrence capacity. In summary, the results we presented show proof of principle that opens new possibilities for further preclinical trials.

Characterization of three classes of membrane proteins involved in fungal azole resistance by functional hyperexpression in Saccharomyces cerevisiae

The study of eukaryotic membrane proteins has been hampered by a paucity of systems that achieve consistent high-level functional protein expression. We report the use of a modified membrane protein hyperexpression system to characterize three classes of fungal membrane proteins (ABC transporters Pdr5p, CaCdr1p, CaCdr2p, CgCdr1p, CgPdh1p, CkAbc1p, and CneMdr1p, the major facilitator superfamily transporter CaMdr1p, and the cytochrome P450 enzyme CaErg11p) that contribute to the drug resistance phenotypes of five pathogenic fungi and to express human P glycoprotein (HsAbcb1p). The hyperexpression system consists of a set of plasmids that direct the stable integration of a single copy of the expression cassette at the chromosomal PDR5 locus of a modified host Saccharomyces cerevisiae strain, ADDelta. Overexpression of heterologous proteins at levels of up to 29% of plasma membrane protein was achieved. Membrane proteins were expressed with or without green fluorescent protein (GFP), monomeric red fluorescent protein, His, FLAG/His, Cys, or His/Cys tags. Most GFP-tagged proteins tested were correctly trafficked within the cell, and His-tagged proteins could be affinity purified. Kinetic analysis of ABC transporters indicated that the apparent K(m) value and the V(max) value of ATPase activities were not significantly affected by the addition of His tags. The efflux properties of seven fungal drug pumps were characterized by their substrate specificities and their unique patterns of inhibition by eight xenobiotics that chemosensitized S. cerevisiae strains overexpressing ABC drug pumps to fluconazole. The modified hyperexpression system has wide application for the study of eukaryotic membrane proteins and could also be used in the pharmaceutical industry for drug screening.

Regulation of MDR1 gene expression in multidrug-resistant cancer cells is independent from YB-1

The MDR1 gene encoded transmembrane ABC-transporter MDR1/P-glycoprotein can mediate the phenotype of multidrug resistance (MDR), a major obstacle in the clinical management of cancer patients. It was hypothesized that YB-1 is a fundamental regulatory factor of the MDR1 gene in tumor cells and can therewith enhance drug resistance. To analyze the potential impact of YB-1 in MDR cancer cells, two specific anti-YB-1 small interfering RNAs (siRNAs) were designed for transient triggering the gene-silencing RNA interference (RNAi) pathway in the MDR cell lines EPG85-257RDB and EPP85-181RDB as well as in their drug-sensitive counterparts EPG85-257P and EPP85-181P. Since both siRNAs showed biological activity, for stable inhibition of YB-1 corresponding tetracycline-inducible short hairpin RNA (shRNA)-encoding expression vectors were designed. By treatment of the cancer cells with these constructs, the expression of the targeted YB-1 encoding mRNA and protein was completely inhibited following tetracycline exposure. These gene-silencing effects were not accompanied by modulation of the MDR1 expression or by reversal of the drug-resistant phenotype. In conclusion, the data demonstrate the utility of the analyzed RNAs as powerful laboratory tools and indicate that YB-1 is not involved in the regulation of the MDR1 gene or the development of the drug-resistant phenotype in MDR cancer cells.

Progress of RNA interference in the therapy of gastric cancer

RNA interference (RNAi) is a new gene-silencing technique, which is a post-transcriptional gene silencing mediated by double-stranded RNA, resulting in the sequence-specific silence of target gene. RNAi technique has been applied widely in the research of various tumors, and most of the results have shown that it could specifically inhibited the expression of oncogenes, cancer-related genes and mutant genes, so as to suppress the occurrence and development of tumors. Meanwhile, explorations have also been performed on the therapy of gastric cancer, and some significant advances have been obtained. RNAi technique can not only act on the target genes directly, but also treat gastric cancer indirectly by restraining the angiogenesis. Furthermore, RNAi technique can be used to resist the multi-drug resistance during chemotherapy.

The application of siRNA technology to cancer biology discovery

RNA interference (RNAi) is a naturally occurring cellular defense mechanism against viral infections and transposon invasion. Short double-stranded RNA molecules, so-called small-interfering (si)RNAs, bind their complementary mRNA leading to the mRNA's degradation. During the past few years, RNAi has become a valuable tool for transient as well as stable repression of gene expression rendering the time-consuming production of knockout animals superfluous. In this chapter the usability of the RNAi technology in cancer research will be described, focusing on the application of large-scale screens for identification of new components in cancer-relevant signal pathways (e.g., p53, RAS). The screens are especially helpful in the detection of potential anticancer drug targets or siRNAs with therapeutic potential.

Reversal of BCRP-mediated multidrug resistance by stable expression of small interfering RNAs

Breast cancer resistance protein (BCRP) is an ATP-binding cassette multidrug transporter that confers resistance to various anticancer drugs like Mitoxantrone. Overexpression of BCRP confers multidrug resistance (MDR) in cancer cells and is a frequent impediment to successful chemotherapy. For stable reversal of BCRP-depending MDR by RNA interference technology, a hU6-RNA gene promoter-driven expression vector encoding anti-BCRP short hairpin RNA (shRNA) molecules was constructed. By treating endogenously and exogenously expresses high levels of BCRP cells with these constructs, expression of the targeted BCRP-encoding mRNA, and transport protein was inhibited completely. Furthermore, the accumulation of mitoxantrone in the anti-BCRP shRNA-treated cells increased. And the sensitivity to mitoxantrone of anti-BCRP shRNA-treated cells is increased 14.6-fold and 2.44-fold respectively compared to their control (P < 0.05). These data indicated that stable shRNA-mediated RNAi could be tremendously effective in reversing BCRP-mediated MDR and showed promises in overcoming MDR by gene therapeutic applications.

Complete reversal of ABCG2-depending atypical multidrug resistance by RNA interference in human carcinoma cells

In the chemotherapeutic treatment of patients with disseminated neoplasms, multidrug resistance (MDR) is a major obstacle. ABCG2 (BCRP/MXR), a member of the superfamily of adenosine triphosphate-binding cassette (ABC) transporters, was demonstrated to be associated with "atypical" forms of multidrug-resistant phenotypes of cancer cells. To overcome the ABCG2-depending MDR, two specific anti-ABCG2 small interfering RNAs (siRNAs) were designed for transient triggering of the gene-silencing RNA interference (RNAi) pathway in the human gastric carcinoma cell line EPG85-257RNOV, exhibiting an atypical MDR phenotype. Because both siRNAs showed biological activity, for stable inhibition of ABCG2 corresponding short hairpin RNA (shRNA) expression vectors were constructed. By treatment of EPG85-257RNOV cells with these constructs, expression of the targeted ABCG2-encoding mRNA and transport protein was inhibited completely. Furthermore, anti-ABCG2 shRNA-treated cells increased cellular drug accumulation to the same level measured in drug-sensitive parental cells. These effects were accompanied by complete reversal of the drug-resistant phenotype. Thus, the data indicate that siRNA- and shRNA-mediated RNAi-based gene therapy may be applicable in preventing and reversing ABCG2-depending atypical MDR.

RNA interference-triggered reversal of ABCC2-dependent cisplatin resistance in human cancer cells

The adenosine triphosphate binding cassette (ABC)-transporter ABCC2 (MRP2/cMOAT) can mediate resistance against the commonly used anticancer drugs cisplatin and paclitaxel. To overcome the ABCC2-depending drug resistance, two specific anti-ABCC2 small interfering RNAs (siRNAs) were designed for transient triggering of the gene-silencing RNA interference (RNAi) pathway in the cisplatin-resistant human ovarian carcinoma cell line A2780RCIS. Since both siRNAs showed biological activity, for stable inhibition of ABCC2 a corresponding short hairpin RNA (shRNA)-encoding expression vector was designed. By treatment of A2780RCIS cells with this construct, the expressions of the targeted ABCC2 encoding mRNA and transport protein were inhibited. These effects were accompanied by reversal of resistance against cisplatin and paclitaxel. Thus, the data demonstrate the utility of the analyzed RNAs as powerful laboratory tools and indicate that siRNA- and shRNA-mediated RNAi-based gene therapeutic approaches may be applicable in preventing and reversing ABCC2-depending drug resistance.

Will technology provide solutions for drug resistance in veterinary helminths?

Drug resistance in veterinary helminths affects a growing number of livestock producers on a global basis. The parasites infecting the major species of livestock are presently showing resistance in varying degrees to the commonly used classes of anthelmintics. The degree and extent of this problem especially with respect to multidrug resistance (MDR) in nematode populations is likely to increase. Finding solutions to the spread of resistance requires knowledge of the drugs' modes of action and mechanisms of resistance. This knowledge can then be applied to detect and monitor the state of resistance. Here we present a brief overview of resistance mechanisms and some of the technologies being used to study them. We also discuss some of the strategies for slowing the spread of resistance. The issue of reversal of drug resistance is analysed under consideration of recent progress in the field of MDR reversal in non-infectious diseases. Finally, we propose an application of currently available technologies that could assist in the detection and monitoring of anthelmintic resistance. Taking into account the significant complexity of the genetic mechanism of anthelmintic resistance in and between the various species, we suggest to undertake a co-ordinated effort to systematically identify anthelmintic-related single nucleotide polymorphisms (SNPs) in the most important helminth parasites. Monitoring the state of resistance in field populations could be achieved with a SNP-based protocol for genotyping the many genes known or suspected to contribute to the modes of action or mechanisms of resistance to the various classes of anthelmintics. If significant associations between genotypes and phenotypes exist within a species, then a single test with sufficient SNPs could potentially have universal applicability. These could then be explored for the development of new molecular diagnostic procedures. New classes of anthelmintics are needed, but until they are developed and available to the producers, technology can assist to achieve the goal of better sustainability in anthelmintic usage.

RNA interference: from gene silencing to gene-specific therapeutics

In the past 4 years, RNA interference (RNAi) has become widely used as an experimental tool to analyse the function of mammalian genes, both in vitro and in vivo. By harnessing an evolutionary conserved endogenous biological pathway, first identified in plants and lower organisms, double-stranded RNA (dsRNA) reagents are used to bind to and promote the degradation of target RNAs, resulting in knockdown of the expression of specific genes. RNAi can be induced in mammalian cells by the introduction of synthetic double-stranded small interfering RNAs (siRNAs) 21–23 base pairs (bp) in length or by plasmid and viral vector systems that express double-stranded short hairpin RNAs (shRNAs) that are subsequently processed to siRNAs by the cellular machinery. RNAi has been widely used in mammalian cells to define the functional roles of individual genes, particularly in disease. In addition, siRNA and shRNA libraries have been developed to allow the systematic analysis of genes required for disease processes such as cancer using high throughput RNAi screens. RNAi has been used for the knockdown of gene expression in experimental animals, with the development of shRNA systems that allow tissue-specific and inducible knockdown of genes promising to provide a quicker and cheaper way to generate transgenic animals than conventional approaches. Finally, because of the ability of RNAi to silence disease-associated genes in tissue culture and animal models, the development of RNAi-based reagents for clinical applications is gathering pace, as technological enhancements that improve siRNA stability and delivery in vivo, while minimising off-target and nonspecific effects, are developed.